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I do not understand how the fact $M$ is maximal is related to $A/M$ being simple.

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  • $\begingroup$ If $I/M$ is a proper non-trivial ideal of $A/M$, what can you say about $\langle I, M \rangle$? $\endgroup$ Commented May 3, 2023 at 2:29
  • $\begingroup$ Provided $M$ is maximal, I can assure $\langle I, M\rangle = A$. Is that right? $\endgroup$ Commented May 3, 2023 at 2:31
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    $\begingroup$ Hint: Think of the correspondence isomorphism theorems. Specifically every proper ideal $J \leq A/M$ is of the form $I/M$ for some proper ideal $I$ of $A$ which contains $M$. $\endgroup$ Commented May 3, 2023 at 2:33
  • $\begingroup$ And can that be possible if $I/M$ is a proper, non-trivial ideal of $A/M$? $\endgroup$ Commented May 3, 2023 at 2:42
  • $\begingroup$ No, we previously stated $I/M$ is non trivial and because of that $I \neq M$. Also, $I \neq A$ because $I/M$ is a proper ideal. Contradiction. $\endgroup$ Commented May 3, 2023 at 2:51

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